The performance of many devices, such as laser printers and optical memories, can be improved with laser arrays having independently controlled lasing elements. For example, laser printers which use an array of lasing elements can have higher printing speeds and better spot acuity than printers with only a single lasing element. In many applications it is important that the array's lasing elements be accurately positioned and oriented.
Monolithic laser arrays usually output light beams having the same wavelength. Typically, that wavelength can only be varied over a small range. However, in some applications, including color printing, it is desirable to output multiple wavelengths that span a wide wavelength range; for example, from the infrared through the visible. In color printing this enables one to match the output laser characteristics to photoreceptor response windows, or to separate overlapping laser beams after scanning by the use of dichroic filters. In other applications it may be desirable to emit multiple laser beams with different polarizations or spot profiles. Finally, it is almost always desirable to have low electrical, optical, and thermal crosstalk between lasing elements.
As compared to present day monolithic laser arrays, nonmonolithic laser arrays can provide a greater range of laser beam characteristics (such as wavelength, polarization and spot sizes) and have lower electrical, optical, and thermal crosstalk. Because of these advantages, there is a need for nonmonolithic laser arrays.
A nonmonolithic laser array usually consists of a plurality of individual laser diodes mounted on a support. Since in many applications the output laser beams must be accurately spaced, the supports for the lasing elements should enable the accurate positioning of the lasing elements. Ideally, the supports should not detract from the advantages of nonmonolithic laser arrays.
Prior art nonmonolithic semiconductor laser arrays usually use planar supports. Laser alignment involves external manipulations of the lasing elements onto the support. Prior art planar laser arrays have a major problem with how close lasing elements can be spaced. Laser stripes are generally placed at the center of the chip to avoid damage to the stripes during cutting of the wafer from which the laser is produced. This limits the achievable minimum spacing between lasing elements if those elements are placed on a common planar substrate.
Kato et al., U.S. Pat. No. 4,901,325, teaches a non-planar nonmonolithic laser array suitable for use with closely spaced lasing elements. A simplified view of that support is shown in FIG. 1. While the support 10 (with a spacer 12) enables the lasing elements 14 to be spaced within microns, absolute control of the lasing element spacing (how close the lasing elements are to their desired location) is not provided for. Further, the orientations of the lasing elements are not rigidly controlled.
Thus, there exists a need for methods and devices that enable close, accurate spacing of lasing elements in a nonmonolithic laser array without excessive thermal, optical, and/or electrical cross-talk. Such methods and devices are even more desirable if they permit the accurate orientation of the lasing elements.